1. Technical Field
This invention relates generally to conveyors, and more specifically to conveyors which are used for feeding raw materials into grinders and hammermills, more particularly a conveyor for use with mobile wood choppers and refuse grinders of the pivot-tub type.
2. Background
The utility of wood choppers and refuse grinders, particularly of the pivot tub type are well known. Also well known in the art is the desirability of providing a means for transporting a grinder or hammermill to an area where material is to be ground or pulverized. See Zehr, U.S. Pat. No. 4,997,135.
It is desirable to provide a means for conveying material to be ground or pulverized to the pivot tub for ultimate presentation to the grinder or hammermill. Conveyor means for use with mobile grinders or hamermills must meet the same requirements as the mill itself for transportation, that being that the apparatus must conform to the rules of the road, particularly in reference to width. Additionally, it is desirable for the apparatus to be capable of being reconfigured to provide a lower profile for transportation.
Conveyors for feeding various hoppers and bins have been described in a number of publications. In Squifflet, U.S. Pat. No. 4,187,047, a silo and elevator structure which is transportable by trailer bed is described. The Squifflet conveyor erects vertically and transports material, in this case an asphalt mix, to a silo which in turn is erected in such a manner so that trucks may be loaded from the silo.
In Brock, U.S. Pat. No. 4,249,351, a self erecting apparatus for transporting and temporarily storing material such as asphalt, including a surge bin, a drag chute and a conveyor for transporting the asphalt to the surge bin is described.
Similarly, in Musil, U.S. Pat. No. 4,482,281, a portable asphalt storage silo with a conveyor assembly including a wheeled frame for transport is described.
While each of these patents describes a transportable conveyor means for use with a hopper or bin, each described invention solves a different set of objectives than those presented by the needs of those who operate transportable hammermills, particularly those of the pivot tub type.
A hammermill consists essentially of a drum having a plurality of impact members affixed to the surface of the drum. The impact members may be in the nature of knives for chopping wood; hammers for pulverizing refuse; or may have other characteristics, depending upon the material to be worked.
The hammermill extends upwardly through the floor of a tub to engage material contained within the tub. Below the hammermill a conveyor is located which removes the pulverized material from the mill. A pivot tub consists of a tub with a cylindrical, rotatable side wall and a non rotatable floor. Typically the tub assembly is mounted to a frame in a manner so that the tub may be pivoted away from the mill so that debris may be cleaned or emptied from the mill. Some means is typically employed for introducing material into the pivot tub.
One problem which typically occurs in the operation of hammermills of this type is that material which is introduced into the tub, upon impact with the hammermill, has a tendency to be violently rejected by the mill and ejected from the tub.
The use of a shield to prevent violent rejection of material from the grinder or hammermill and the associated potential for injury from such flying debris is discussed in Zehr, U.S. Pat. No. 4,997,135. However, the use of such a shield does not prevent entirely, the possibility of such flying debris.
What is needed then, is a means for introducing material which is to be ground or pulverized into the pivot tub of the hammermill, which will provide some means for preventing the materials so introduced from being violently rejected from the mill. In addition, the conveyor means, while it should extend over and above the pivot tub of the hammermill, it should be configured such that it is capable of being retracted from that position so that the pivot tub of the hammermill can be pivoted away from the floor of the mill to facilitate cleaning and servicing the mill.
Additionally, the conveyor means should be readily transportable.